National Sleep Foundation

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Chapter 1: Normal Sleep

Sleep Assessment & Evaluation: Sleep Center / Lab Tools

Sleep disorder centers and sleep labs use subjective tools such as patient interviews, questionnaires, and sleep diaries, as well as a range of objective tests, including:

Polysomnography (PSG)122

PSG is a diagnostic test that requires the patient to sleep in the lab overnight while their sleep behavior is monitored via sensors placed on their body. The sessions are monitored by a technician and usually are recorded on video. PSG monitors a number of physiologic variables during both sleep and wakefulness, including:

In an MSLT is a “napping” test, in which the individual’s brain electrical activity, eye movements, and changes in chin muscle tonus are recorded during 4-5 daytime rest periods, each lasting 20 minutes, spaced 2 hours apart. Both sleep latency (how fast a person falls asleep) and types of sleep are recorded to measure the patient’s degree of daytime sleepiness and the presence or absence of rapid eye movement (REM) periods at sleep onset.

Normally-alert adults take an average of 12 minutes to fall asleep on the MSLT. A patient that consistently falls asleep in less than 5 minutes is deemed to be “pathologically sleepy.” This sleepiness may be stem from the patient lacking time to sleep or from disturbed sleep (i.e., due to restless legs syndrome or disordered breathing).

Maintenance of Wakefulness Test (MWT)

The MWT is a variant of the MSLT; it measures the individual’s ability to stay awake under conditions that would usually cause sleepiness. For the MWT, patients typically sit in the dark for 20 or 40 minutes in 2-hour increments throughout the day. To be deemed to be “adequately alert,” an individual must be able to stay awake for an average of at least 11 minutes during the MWT. More than 75 percent of normal adults can stay awake for the MWT’s entire 40 minutes.

The MWT helps assess whether an individual’s inability to stay awake risks compromising either his or her safety or someone else’s (i.e., inability to stay awake while driving). The MWT is also used to assess treatment for excessive sleepiness, like the use of stimulant medications.

A wrist actigraph is a small watch-like device that monitors wrist movements throughout the patient’s routine daily activities over a one- to two-week period. The wrist actigraph stores the frequency of the person’s arm movements per minute, and then analyzes the movements to estimate time spent sleep vs. awake. (It uses the fact that we move less when we are asleep than when we are awake.) Wrist actigraphy provides a fair (although not exact) measurement of when, and for how long, a patient sleeps. (See Figure 1.10.) A number of commercially available fitness, sleep, and activity monitors provide similar information.